A steel structure has advantageously flexibility in the space and superior structural stability and durability, as compared with a reinforced concrete structure. However, since a slab is placed on top of the steel beam, the entire story height increases disadvantageously. In order to solve this problem, various slim floor systems have been proposed and utilized, in which a slab is installed within the depth of the steel beam.
In the slim floor system, as illustrated in FIGS. 8 and 9, a slab employs a deep deck plate 20 or a hollow core precast concrete slab and, in order to support the slab, includes a asymmetrical steel beam where the width of the lower flange of the steel beam 10 is expanded. This is similar to a composite slab structure consisted of a deck plate and a concrete slab. However, dissimilar to the general composite slab, a plate 12 is additionally welded to the lower flange 11 of an H-shaped steel or angular steel pipe so that the deck plate is placed above the plate welded to the lower flange, to thereby reduce the story height. In case of this composite beam-slab system, the story height can be efficiently reduced, but applicable slab systems are restricted and thus the height of the composite beam-slab is limited. Therefore, it embraces limitation in the constructible span.
On the other hand, similarly the home-developed composite beam-slab system to reduce the story height has inconveniency such as a weak effect of reducing the story height and a lower applicable efficiency in fabrication of the steel beam and installation thereof. Moreover, due to the recent increase in the steel material price, there is a need to provide a composite beam-slab system capable of sufficiently utilizing a relatively inexpensive concrete, rather than a composite slab system using only the steel structure.